Clinical syndrome associated with defective or deficient von Willebrand factor; factor VIII antigen/von Willebrand factor ratio is low. Disorder causes bleeding prolonged bleeding time (esp. with concomitant aspirin use) and results in bleeding at skin and mucous membranes. PT is normal, and PTT may be prolonged or normal if factor VIII level > 30%. Platelet count and shape are usu. normal, but variant forms associated with angiodysplasia and mild thrombocytopenia are known; platelet aggregation is normal. Ristocetin-induced platelet agglutination is impaired. Condition may be either autosomal dominant or recessive.